Cellulose with adhesive spots on both sides thereof in non-registering relationship as insulating material for electrical apparatus



Aug. 31, 1965 w. s. GRIMES 3,203,823

CELLULOSE WITH ADHESIVE SPOTS ON BOTH SIDES THEREOF IN NON-REGISTERINGRELATIONSHIP AS INSULATING MATERIAL FOR ELECTRICAL APPARATUS Filed Dec.4, 1961 INVENTOR. WILLIAM S. GRI MES ATTORNEY United States Patent3,203,823 CELLULUSE WITH ADHESEVE SPUTS 9N BGTH SIDES THEREGF fNWilli-REGISTERING RELA- TIONSHIP AS INSULATENG MATERIAL FOR ELECTRICALAPPARATUS William S. Grimes, ()livette, Mo, assignor to Qrchard PaperCompany, St. Louis, Mo., a corporation of Missouri Filed Dec. '4, 1961,Ser. No. 156,904 9 'Claims. (Cl. 11738) This invention relates ingeneral to dieiectrics, and,

more particularly, to certain new and useful improvements in insulatingmaterial for use in electrical apparatus.

It is an object of the present invention to provide in sulating materialfor electrical apparatus, such as, elec trical transformers, which isadapted to substantially eliminate corona effect.

It is a further object of said invention to provide insulating materialof cellulosic character for use in electrical apparatus, such as,electric transformers which are designed to contain liquid dielectrics,which material is adapted to provide effective and reliable adhesionbetween sections of said material as well as between same and electricalconductors, such as, transformer coils, to form an integrated,intimately bonded unit.

It is a further object of the present invention to provide insulatingmaterial of cellulosic sheet character for electric transformersutilizing liquid dielectrics, which material is adapted to allow forsubstantially complete liquid penetration in minimum time for completesaturation thereby.

It is an additional object of the present invention to provideinsulating material of cellulosic sheet character adapted primarily foruse with electric transformers, which material may be most economicallyproduced; which may be efficiently and expeditiously integrated intotransformers; and which has proved durable and reliable in usage.

Other objects and details of the invention will be apparent from thefollowing description, when read in connection with the accompanyingdrawing in which FIGURE 1 is a plan View of a sheet of insulatingmaterial constructed in accordance with and embodying the presentinvention, showing the adhesive units on the opposite face of said sheetin dotted lines.

FIGURE 2 is a vertical transverse section taken on the line 2-2 ofFIGURE 1.

FIGURE 3 is a vertical transverse sectional view taken substantially onthe line 2-2 of FIGURE 1 but illustrating the union between two sheetsof the insulating material of the present invention.

Referring now by reference numerals to the drawing which illustrates thepreferred embodiment of the present invention, A designates a sheet orsection of cellulosic insulating material adapted for use in electricalapparatus, such as, particularly, electric transformers utilizing aliquid dielectric, such as, oil. Sheet A is fabricated of kraft, woodpulp, rope, rag, or mixtures of these papermaking fibres, having adesired thickness within the range of 3 to 20 mils, and being ofrelatively high density. The term high density as used in the paperindustry to qualify cellulosic material indicates an actual density orspecific gravity of between .9 and 1.05.

The opposite faces, throughout their extent, of sheet A arediscontinuously coated with adhesive material, such as, shellac, epoxyresins, phenolics, urethanes, polyvinyl,

formal resins, etc., all of which are well known in the art, and withthe coating on each such face being constituted of a multiplicity ofdiscrete adhesive units 1 each of which is entirely surrounded by anuntreated zone 2 with 3,203,823 Patented Aug. 31, 1965 ice the maximumdistance across such zone 2, between adjacent adhesive units 1 beingless than the narrowest dimension of each such unit 1 for purposespresently appearing. The adhesive units 1 on one side of said sheet Aare not in full registry alignment with the adhesive units 1 on theopposite side of said sheet A and are thus in, what might be termed,offset relationship. However, in view of the fact that the interveningdistance between adjacent adhesive units 1 on each face of sheet A isless than the narrowest dimension of such units 1 there will,understandably, be a limited or a partial overlying relationship betweenthe units 1 on the opposite faces of each sheet A, which is critical inthe present invention.

Said adhesive units 1 are applied in a predetermined pattern wherein thesame are arranged in rows, the longitudinal axes of which form an angleof less than degrees with the edge of the sheet extending relatively inthe same general directions as the said rows, so that, for example, inFIGURE 1 the edge 3 of sheet A would be the line of reference. It willbe seen that with the adhesive units so arranged the rows on one side ofsaid sheet will tend to cross the rows on the opposite side of the sheetA to thus assure against registry. If adhesive units 1 were arranged inrows having an axis of 45 degrees with the reference edge, it is quitepossible that there could result an undesired registry or alignmentbetween adhesive units 1 on the opposite sides of the sheet. Althoughangles of less than 45 degrees will substantially prevent such registry,it has been found that rows which form an angle of approximately 23degrees which the reference edge are preferable as the same provides anoverlap of the adhesive units 1 on opposite sides of sheet A of about16% when the adhesive units 1 comprise about 36% of the total area ofthe related faces of sheet A.

Each face of the sheet A is thus provided with untreated areas whichform a grid having both longitudinally and transversely extendingportions; with the same being at right angles to each other.Furthermore, the longitudinal portions extend along axes which are atacute angles to the longitudinal margins of the sheet and the transverseportions are along axes which form acute angles with the transversemargins of the sheet. Additionally, with reference to FIGURE 1, it willbe noted that the longitudinal portions of the untreated grid on 0 oneface of sheet A are in intersecting relationship to the longitudinalportions of the untreated grid on the other face of said sheet A and thetransverse portions of each such grid are in like relationship.

Thus, the pattern of adhesive units and the related grid on one face ofsheet A are so related to the pattern and grid on the opposite face ofsheet A as to prevent any undesired registration with the faces of othersheets to be laminated or otherwise secured to either face of said sheetA.

The total area of adhesive units 1 on any one face of sheet A shouldpreferably constitute between 25 and of the total area of such sheetface, although, as indicated, it has been found that coverage within themedian of said range such as, between 36% and 38%, is preferable.Consonant with practices heretofore accepted in the field of transformerpaper adhesives, approximately 5 pounds of the adhesive for every 3,000square feet of surface to be coated is utilized. With sheets of thepresent invention, it will be seen that with 5 pounds of adhesive beingutilized, the thickness of each adhesive unit 1 would be /2 mil for a50% coverage and 1 mil if only 25% of the area were covered. Therefore,with coverage in the preferred median range of 36% to 38%, the thicknessof each adhesive unit would be approximately 4 mil.

The adhesive unit 1 may be of various contours but,

for purpose of illustration only, said units l are illustrated in thedrawing as being of square character, and, in this instance, are inch byinch, being formed on as inch centers. However, it is obvious thatcircular, rectangular, triangular, polygonal, and other configurationsmay be as easily utilized. Adhesive units 1 may be applied upon sheetsof paper by any suitable means but the use of gravure rollers haveproved most efficient.

Sheets A are especially adapted for use in the formation of transformercores and are incorporated therein in the customary manner whereby aplurality of such sheets A, such as the two shown in FIGURE 3, areplaced in face-to-face relationship, to form a basic set, andconventional transformer coils (not shown), which have been preferablyvarnish coated, are applied against the outer or exposed face of eachsheet of said set and then the exposed sides of the said coils haveapplied thereagainst a set of said sheets so that the core is built upto the extent desired by alternating sets of said sheets and transformercoils. It is, of course, to be recognized that the said sets of saidsheets A may be comprised of any number of said sheets, as the two shownin FIGURE 3 are merely for purposes of illustration. Furthermore, it isto be recognized that the cores so formed may be of any desired contour,such as, square, rectangular, annular, etc., since the sheets A areequally adapted for any such design.

After the components of the core to be formed have been assembled asdescribed above, the unit is then subjected to a baking operation withthe temperature reaching approximately 300 F., and with such operationcontinuing for about one hour. The said baking thus effects a curing ofthe adhesive material used to provide adhesive units 1 for the purposeof effecting a bonding between sheets A and a bonding between the sheetsand the transformer coils. The thickness of the adhesive coating, beingapproximately mil, allows of a relatively thick cradle-formation withrespect to the wires of the transformer coils so as to bring about apositive, reliable bond between the sheets A and said coils. Asindicated above, the particular adhesive may be of any well-knowncharacter such as suggested above, although a 35% shellac solution or a50% epoxy varnish have been found in actual practice to be mostsatisfactory.

Subsequent to, or simultaneous with, the baking operation, the core isthen subjected to evacuation for air removal, and upon termination ofsuch procedure, the core is then immersed in an oil bath for oilpenetration. The unique, novel construction of sheets A substantiallyprevents the development of air pockets so that the oil will penetratethe said sheets A with maximum thoroughness. Thus, with the eliminationof air entrapment there is a consequent prevention of corona effectduring operation of the transformer so that the effectiveness thereof aswell as its life is measurably enhanced.

Referring now to FIGURE 3, the critical nature of the offsetrelationship of the adhesive units on one face of sheet A to those onthe opposite face becomes quite apparent when it is recognized that eachsuch adhesive unit 1 is confronted by a limited portion of adhesive unitor units and a substantially large untreated zone 2 on the face of thesheet applied thereagainst to form a set disposed between adjacenttransformer coils. Heretofore the adhesive portions of one sheet hadbeen applied fully, coextensively upon the adhesive areas of acornpanion sheet so that an adhesively treated area was not brought intoface-to-face relationship with an untreated portion. By such heretoforeutilized arrangement, there were expectedly formed a considerable numberof air pockets which prevented full oil penetration and which wereproductive of corona effect during transformer operation. With thesheets A of the present invention, the oil is not present in areashighly resistant to penetration since the extent of adhesiveunit-to-adhesive unit relationship is very small wherefore the oil mayflow readily between the opposed sheets A as well as within the sheets Abetween the adhesive units 1 on the opposite faces thereof so thatcomplete saturation is achieved.

Thus, in view of the foregoing, it is apparent that the highly novelcharacter of the discontinuous coating of the insulating material of thepresent invention provides the necessary, reliable bonding betweeninsulation sheets as well as between the same and transformer coils, aswell as being permissive of maximum, thorough oil saturation so that atransformer core formed therefrom will be free of corona effect. SheetsA may be most economically produced and may be most readily incorporatedin transformer cores. The said sheets A are adapted for utilization withother types of electrical apparatus but the peculiar adaptation of thesame for electrical transformers has been described hereinabove forpurposes only of demonstrating the uniqueness of the present invention.

It should be understood that changes and modifications in the formation,construction, arrangement, and combination of the several parts of theinsulating material for electrical apparatus may be made and substitutedfor these herein shown and described without departing from the natureand principle of my invention.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. Insulating material for electrical apparatus comprising a sheet ofcellulosic material, areas of each side of said sheet being treated byhaving applied thereon a plurality of discrete adhesive units, theuntreated areas of each side of said sheet forming a grid havinglongitudinal and transverse portions, the longitudinal and transverseportions of said grid being at right angles to each other, thelongitudinal portions being at an acute angle to the longitudinalmargins of said sheet and the transverse portions of said grid being atan acute angle to the transverse margins of said sheet.

2. Insulating material for electrical apparatus as defined in claim 1and further characterized by the adhesive units on one face of saidsheet being in non-registering partial-overlying relationship withrespect to the adhesive units on the opposite side of the sheet.

3. Insulating material for electrical apparatus as defined in claim land further characterized by the combined area of the coated portion ofeach face of said sheet being between 25% and 50% of the total area ofeach sheet face.

4. Insulating material for electrical apparatus as defined in claim 1wherein the adhesive units on each face of said sheet coverapproximately 35% to 40% of the total area of the respective face ofsaid sheet.

5. Insulating material for electrical apparatus comprising a sheet ofcellulosic material and a plurality of discrete unconnected adhesiveunits applied on each face of said sheet to thereby form a discontinuousadhesive coating, the adhesive units on each face of said sheet being inspaced apart relationship with the intervening portions of said sheetbeing untreated, the adhesive units on one face of said sheet being inpartial overlying but nonregistering relationship with respect to theadhesive units on the opposite face of said sheet, the adhesive units oneach face of said sheet jointly covering approximately 35% to 40% of thetotal area of the respective face of said sheet the untreated portion ofeach face of said sheet forming a grid having longitudinal andtransverse portions, said longitudinal and transverse portions of saidgrid being at right angles to each other and at acute angles to thelongitudinal and transverse margins of said sheet respectively.

6. Insulating material for electrical apparatus as defined in claim 1and further characterized by the longitudinal and transverse portions ofthe grid on one side of said sheet being in intersecting relationshipwith the longitudinal and transverse portions respectively of the gridon the other side of said sheet.

7. Insulating material for electrical apparatus as de fined in claim 1and further characterized by the said longitudinal and transverse gridportions being at an angle of less than 45 degrees to the longitudinaland transverse margins of said sheet respectively.

8. Insulating material for electrical apparatus comprising a sheet ofcellulosic material, areas of each side of said sheet being treated byhaving applied thereon a plurality of discrete adhesive units, theuntreated areas of each side of said sheet forming a grid havinglongitudinal and transverse portions at right angles to each other, thelongitudinal portions of each grid being at an acute angle to thelongitudinal margins of the sheet, the transverse portions of each gridbeing at an acute angle to the transverse margins of the sheet, theadhesive units on one side of said sheet being in off-set,non-registering relationship with respect to the adhesive units on theopposite side of the sheet, the longitudinal portions of the grid on oneside of said sheet being in non-parallel, intersecting relationship withrespect to the longitudinal portions of the grid on the opposite side ofsaid sheet, and the transverse portions of the grid on one side of saidsheet being in non-parallel, intersecting relationship with respect tothe transverse portions of the grid on the other side of said sheetwhereby when a plurality of said sheets are applied in layer formationimpregnation of said sheets is facilitated through substantial obviationof the development of air pockets.

9. Insulating material for electrical apparatus as defined in claim 8and further characterized by the longitudinal and transverse portion-sof the grids on each side of said sheet being at approximately an angleof 23 degrees to the longitudinal and transverse margins respectively ofsaid sheet.

References Cited by the Examiner UNITED STATES PATENTS 2,264,629 12/41Engert et a1. Q. 117-14 2,396,391 3/46 Ross 117-14 3,065,101 11/62Phipps 24-67.1

RICHARD D. NEVIUS, Primary Examiner.

EARL M. BERGERT, Examiner.

1. INSULATING MATERIAL FOR ELECTRICAL APPARATUS COMPRISING A SHEET OFCELLULOSIC MATERIAL, AREAS OF EACH SIDE OF SAID SHEET BEING TREATED BYHAVING APPLIED THEREON A PLURALITY OF DISCRETE ADHESIVE UNITS, THEUNTREATED AREAS OF EACH SIDE OF SAID SHEET FORMING A GRID HAVINGLONGITUDINAL AND TRANSVERSE PORTIONS, THE LONGITUDINAL AND TRANSVERSEPORTIONS OF SAID GRID BEING AT RIGHT ANGLES TO EACH